Honestly, I just kind of stumbled into Hubpages via some work search engines (currently unemployed thanks to a company layoff).
However, I've always been interested in writing articles with pertinence to my interests and fields of college study (Technology/Games).
So, I decided to just start writing whatever came to mind, which quickly became a decent sized log of ideas.
I've won awards in the past for poetry and fiction, so writing isn't new to me, but publishing is. That being said, so far I've only published 4 hubs, but have enjoyed writing them and researching for them. In the meantime I'm still looking for work but hoping that if I can pump out enough articles (1-2 daily is what I want to do) I could make some side money here. Even if it isn't much.
To be more concise and in addressing the topic question: I started because I felt like it. Because it could hold the possibility of making some money, and because it's a nice (and FREE) hobby to have as well.